American Megatrends MegaRAID Express 500 - Manual (Page 26)

MegaRAID Express 500 Hardware Guide 12
Parity
Parity generates a set of redundancy data from two or more parent data sets. The
redundancy data can be used to reconstruct one of the parent data sets. Parity
data does not fully duplicate the parent data sets. In RAID, this method is
applied to entire drives or stripes across all disk drives in an array. The types of
parity are:
Type Description
Dedicated Parity The parity of the data on two or more disk drives is
stored on an additional disk.
Distributed
Parity
The parity data is distributed across all drives in the
system.
If a single disk drive fails, it can be rebuilt from the parity and the data on the
remaining drives.
RAID level 3 combines dedicated parity with disk striping. The parity disk in
RAID 3 is the last logical drive in a RAID set.
RAID level 5 combines distributed parity with disk striping. Parity provides
redundancy for one drive failure without duplicating the contents of entire disk
drives, but parity generation can slow the write process. A dedicated parity
scheme during normal read/write operations is shown below: